Fuel cells are devices that directly convert chemical energy of reactants, i.e., fuel and oxidant, into direct current (DC) electricity. A common fuel for fuel cells is hydrogen gas, which can be stored in compressed form or stored in a hydrogen absorbent material, e.g., lanthanum nickel alloy, LaNi5H6, or other hydrogen absorbent metal hydrides. Hydrogen can also be produced on demand by chemical reaction between a chemical metal hydride, such as sodium borohydride, NaBH4, and water or methanol.
In a chemical metal hydride reaction, a metal hydride such as NaBH4, reacts as follows to produce hydrogen:NaBH4+2H2O→(heat or catalyst)→4(H2)+(NaBO2)
Half-reaction at the anode:H2→2H++2e−
Half-reaction at the cathode:2(2H++2e−)+O2→2H2O
Suitable catalysts for this reaction include cobalt, platinum and ruthenium, and other metals. The hydrogen fuel produced from reforming sodium borohydride is reacted in the fuel cell with an oxidant, such as O2, to create electricity (or a flow of electrons) and water by-product. Sodium borate (NaBO2) by-product is also produced by the reforming process. A sodium borohydride fuel cell is discussed in U.S. Pat. No. 4,261,956, which is incorporated by reference herein in its entirety. The hydrogen produced by chemical metal hydrides may be compressed or stored in a metal hydride hydrogen absorbent material for later consumption by a fuel cell.
One disadvantage of the known hydrogen gas generators using chemical hydride as fuel is that the separation of the hydrogen gas resulting from the reaction is not always complete. Over time, water, water vapor, reaction agents, and reaction by-products may pass from the gas generator to the fuel cell reducing the fuel cell's efficiency and operational life.
Accordingly, there is a desire to obtain a hydrogen gas generator apparatus with a membrane assembly that effectively separates the resulting hydrogen gas from the reaction solutions.